This invention relates generally to vapor recovery systems associated with the refueling of vehicles. More particularly, this invention relates to a modification made to an assist type of vapor recovery system to improve the performance and compatibility of the system when it is used for refueling vehicles that have on board refueling vapor recovery (ORVR) systems.
In fuel dispensing systems, such as those used for delivering gasoline to the fuel tank of a vehicle, environmental protection laws require that vapors emitted from the tank during the fuel dispensing process be recovered. Fuel is customarily delivered through a nozzle via a fuel hose and vapors are recovered from the nozzle via a vapor hose that conveys the vapor to the storage tank from whence the fuel came. In what is referred to as a balanced system, the vapors are forced through the vapor hose by the positive pressure created in the vehicle tank as the fuel enters it. In other systems, referred to as assist-type systems, the vapor is pumped from the vehicle tank and forced into the storage tank by a vapor recovery system connected to the vapor hose. Currently, many fuel dispensing pumps at service stations are equipped with vacuum assisted vapor recovery systems that collect fuel vapor vented from the fuel tank filler pipe during the fueling operation and transfer the vapor to the fuel storage tank.
Recently, onboard, or vehicle carried, fuel vapor recovery and storage systems (commonly referred to as onboard refueling vapor recovery or ORVR) have been developed in which the head space in the vehicle fuel tank is vented through a charcoal-filled canister so that the vapor is absorbed by the charcoal. Subsequently, the fuel vapor is withdrawn from the canister into the engine intake manifold for mixture and combustion with the normal fuel and air mixture. The fuel tank head space must be vented to enable fuel to be withdrawn from the tank during vehicle operation. In typical ORVR systems, a canister outlet is connected to the intake manifold of the vehicle engine through a normally closed purge valve. The canister is intermittently subjected to the intake manifold vacuum with the opening and closing of the purge valve between the canister and intake manifold. A computer which monitors various vehicle operating conditions controls the opening and closing of the purge valve to assure that the fuel mixture established by the fuel injection system is not overly enriched by the addition of fuel vapor from the canister to the mixture.
Fuel dispensing systems at service stations having vacuum assisted vapor recovery capability which are unable to detect ORVR systems waste energy, increase wear and tear, ingest excessive air into the underground storage tank and cause excessive pressure buildup in the piping and underground storage tank due to the expanded volume of hydrocarbon saturated air.
Refueling of vehicles equipped with ORVR can be deleterious for both the vapor recovery efficiency of a vapor recovery system and the durability of some system components. The refueling of an ORVR equipped vehicle deprives the vapor recovery system of any gasoline vapors intended to be returned to the storage tank, typically located underground. In lieu of having gasoline vapor available, the vapor pump of an assist-type system will pump air back into the storage tank. The air pumped back into the storage tank vaporizes liquid fuel that is in the storage tank, pressurizes the ullage space of the storage tank and is then vented to the atmosphere as polluting emissions.
One of the known types of vapor recovery systems that attempts to avoid these problems is the balance type of vapor recovery system. The balance system does not use a vapor pump, but simply allows the free exchange of vapor between the gasoline tank of the vehicle being refueled and the storage tank. Since the balance system does not allow air to be induced into the storage tank when refueling an ORVR equipped vehicle, the vapor growth problem is avoided and, in fact, the storage tank pressures are typically reduced by the removal of liquid and possibly vapor. The reduction in vapor flow rate when refueling an ORVR vehicle is about 100% (i.e., no vapor or air flow to the storage tank).
One known type of assist vapor recovery system attempts to avoid the storage tank pressurization problem by sensing the presence of an ORVR equipped vehicle during refueling and uses this information to turn off the vapor pump during the refueling of an ORVR vehicle. The systems ability to recognize an ORVR system and adjust the fuel dispenser's vapor recovery system accordingly eliminates the redundancy associated with operating two vapor recovery systems for one fueling operation. One example of this type of system is described in U.S. Pat. No. 5,782,275 issued to Gilbarco and hereby incorporated by reference. The reduction in vapor or air flow rate during an ORVR refueling will be 100% when the vapor pump is turned off; however, some initial run time is required for the pressure sensor to activate and turn the pump off. The particular system described in the '275 patent utilizes a hydrocarbon sensor to determine if an ORVR fueling event is occurring. If so, a signal from the sensor turns the vapor pump on/off.
Another example of an assist vapor recovery system is described in U.S. Pat. No. 6,095,204 issued to Healy and hereby incorporated by reference. The system of the '204 patent uses a pressure sensor in place of the hydrocarbon sensor to determine if an ORVR refueling event is taking place and subsequently turn the vapor pump on/off. Therefore, an overall reduction of only about 75% is typical for such a system.
Another type of known assist system utilizes a vapor flow restrictor built into the nozzle to decrease the vapor flow back to the storage tank during an ORVR refueling event. The nozzle for such a system utilizes a flexible boot to engage the filler neck of a vehicle, but unlike a balance system, an air-tight seal is prevented. If an air-tight seal were present when a vapor pump is being used in conjunction with an ORVR vehicle, relatively high vacuum levels develop within the vapor space of the nozzle. These abnormally high vacuum levels cause abnormal operation of the automatic shut-off mechanism in the nozzle. The nozzle for such a system utilizes either a check valve or holes in the boot itself to limit the amount of vacuum to which the nozzle is exposed. Such vacuum relief measures allow the vacuum level to increase to a detectable level within the nozzle and the elevated vacuum level is used to operate a flow restrictor in the vapor flow path. The exact reduction in vapor (air) flow rate during an ORVR refueling with such a system is from 25% to 78% depending on the exact configuration and fueling flow rate.
Another type of assist system is described in U.S. Provisional Patent Application Ser. No. 60/461,097 filed Apr. 8, 2003 and assigned to the assignee of this invention. That system utilizes an assist-type of nozzle and a balance-type flexible boot to seal against the filler neck of the vehicle being refueled. This arrangement results in relatively high vacuum levels in the nozzle vapor space. To account for those vacuum levels, the shut-off mechanism is modified. Since the nozzle boot is sealed against the vehicle's filler neck, the vapor recovery system will not ingest any air into the storage tank. The vapor flow rate will not be reduced completely 100% as with a balance system because the vapor pump will be capable of pumping some vapor from the vehicle's fuel tank. The reduction in vapor flow rate is typically about 90% with such a system.
The above-described assist vapor recovery system effectively blocks the inlet or nozzle end of the vapor hose resulting in relatively high vacuum levels in the vapor hose itself. The system described in the '204 patent does so similarly, but to a lesser degree. The vacuum levels in the vapor hose during refueling of an ORVR vehicle will be about ten times higher than the vacuum levels in the vapor hose when refueling a non-ORVR equipped vehicle. In addition, elevated vacuum levels will be present in the entire length of the vapor hose due to the drastically reduced vapor flow rate. The exterior of the vapor hose is also subjected to the fluid pressure since typically the fluid carrying hose surrounds it in a coaxial arrangement. The exterior pressure combined with the elevated interior vacuum levels presents a condition that will promote the collapse of the vapor hose tubing.
Moreover, the current trends in the industry are to increase the amount of ethanol used in gasoline fuel blends which decreases the mechanical properties of the material used in the vapor hose tubing. These factors, in combination with market movements toward single hose dispensers which increases the flexing cycle on the vapor hose tubing, result in the collapse and/or failure of the vapor hose tubing. Such problems could become systematic and present a significant issue that must be addressed.